Transmissions comprising a rotary input member, a rotary output member and a housing are known in different forms, comprising for example gear wheels or friction wheels. However, in the case of a gear wheel transmission, the level of efficiency thereof cannot be enhanced to a material degree, as a result of the friction which occurs between the meshing teeth of the gear wheels. In the case of friction wheel transmissions of conventional design configuration on the other hand, high pressure forces as between the co-operating friction wheels are required.